The present subject matter relates generally to linear compressors, such as linear compressors for refrigerator appliances.
Certain refrigerator appliances include sealed systems for cooling chilled chambers of the refrigerator appliances. The sealed systems generally include a compressor that generates compressed refrigerant during operation of the sealed systems. The compressed refrigerant flows to an evaporator where heat exchange between the chilled chambers and the refrigerant cools the chilled chambers and food items located therein.
Recently, certain refrigerator appliances have included linear compressors for compressing refrigerant. Linear compressors generally include a piston and a driving coil. A voltage excitation induces a current within the driving coil that generates a force for sliding the piston forward and backward within a chamber. During motion of the piston within the chamber, the piston compresses refrigerant. Motion of the piston within the chamber is generally controlled such that the piston does not crash against another component of the linear compressor during motion of the piston within the chamber. Such head crashing can damage various components of the linear compressor, such as the piston or an associated cylinder. While head crashing is preferably avoided, it can be difficult to accurately control a motor of the linear compressor to avoid head crashing.
Accordingly, a method for operating a linear compressor with features for avoiding head crashing would be useful. In particular, a method for operating a linear compressor with features for avoiding head crashing without utilizing a position sensor would be useful.
The present subject matter provides a method for operating a linear compressor. The method includes establishing a set of predictors, and establishing a model for an estimated head clearance of the linear compressor with the set of predictors. Coefficients of the model for the estimated head clearance of the linear compressor may also be established. Additional aspects and advantages of the invention will be set forth in part in the following description, or may be apparent from the description, or may be learned through practice of the invention.
In a first exemplary embodiment, a method for operating a linear compressor is provided. The method includes supplying a motor of the linear compressor with a time varying voltage having a peak motor voltage and an excitation frequency, measuring a peak motor current of the linear compressor while the time varying voltage is supplied to the motor of the linear compressor, and calculating an observed minimum velocity of the motor of the linear compressor and an observed stroke length of the motor of the linear compressor using an electrical dynamic model for the motor of the linear compressor and a robust integral of the sign of the error feedback. A set of predictors include the peak motor voltage, the excitation frequency, the peak motor current, the observed minimum velocity and the observed stroke length. The method also includes removing redundant predictors from the set of predictors in order to establish a reduced set of predictors, establishing a model for an estimated head clearance of the linear compressor with the reduced set of predictors, and establishing coefficients of the model for the estimated head clearance of the linear compressor.
In a second exemplary embodiment, a method for operating a linear compressor is provided. The method includes supplying a motor of the linear compressor with a time varying voltage having a peak motor voltage and an excitation frequency, measuring a peak motor current of the linear compressor while the time varying voltage is supplied to the motor of the linear compressor, calculating an observed minimum velocity of the motor of the linear compressor and an observed stroke length of the motor of the linear compressor, and establishing a set of predictors. The set of predictors includes the peak motor voltage, the excitation frequency, the peak motor current, the observed minimum velocity, the observed stroke length, a product of the peak motor voltage and the excitation frequency, a product of the peak motor voltage and the observed stroke length, and a product of the excitation frequency and the observed minimum velocity. The method also includes establishing a model for an estimated head clearance of the linear compressor by conducting a best subsets regression with the set of predictors and establishing coefficients of the model for the estimated head clearance of the linear compressor.
These and other features, aspects and advantages of the present invention will become better understood with reference to the following description and appended claims. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.
A full and enabling disclosure of the present invention, including the best mode thereof, directed to one of ordinary skill in the art, is set forth in the specification, which makes reference to the appended figures.
Reference now will be made in detail to embodiments of the invention, one or more examples of which are illustrated in the drawings. Each example is provided by way of explanation of the invention, not limitation of the invention. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope or spirit of the invention. For instance, features illustrated or described as part of one embodiment can be used with another embodiment to yield a still further embodiment. Thus, it is intended that the present invention covers such modifications and variations as come within the scope of the appended claims and their equivalents.
In the illustrated exemplary embodiment shown in
Within refrigeration system 60, refrigerant flows into compressor 64, which operates to increase the pressure of the refrigerant. This compression of the refrigerant raises its temperature, which is lowered by passing the refrigerant through condenser 66. Within condenser 66, heat exchange with ambient air takes place so as to cool the refrigerant. A fan 72 is used to pull air across condenser 66, as illustrated by arrows AC, so as to provide forced convection for a more rapid and efficient heat exchange between the refrigerant within condenser 66 and the ambient air. Thus, as will be understood by those skilled in the art, increasing air flow across condenser 66 can, e.g., increase the efficiency of condenser 66 by improving cooling of the refrigerant contained therein.
An expansion device (e.g., a valve, capillary tube, or other restriction device) 68 receives refrigerant from condenser 66. From expansion device 68, the refrigerant enters evaporator 70. Upon exiting expansion device 68 and entering evaporator 70, the refrigerant drops in pressure. Due to the pressure drop and/or phase change of the refrigerant, evaporator 70 is cool relative to compartments 14 and 18 of refrigerator appliance 10. As such, cooled air is produced and refrigerates compartments 14 and 18 of refrigerator appliance 10. Thus, evaporator 70 is a type of heat exchanger which transfers heat from air passing over evaporator 70 to refrigerant flowing through evaporator 70.
Collectively, the vapor compression cycle components in a refrigeration circuit, associated fans, and associated compartments are sometimes referred to as a sealed refrigeration system operable to force cold air through compartments 14, 18 (
Turning now to
A piston assembly 114 with a piston head 116 is slidably received within chamber 112 of cylinder assembly 111. In particular, piston assembly 114 is slidable along a first axis Al within chamber 112. The first axis Al may be substantially parallel to the axial direction A. During sliding of piston head 116 within chamber 112, piston head 116 compresses refrigerant within chamber 112. As an example, from a top dead center position, piston head 116 can slide within chamber 112 towards a bottom dead center position along the axial direction A, i.e., an expansion stroke of piston head 116. When piston head 116 reaches the bottom dead center position, piston head 116 changes directions and slides in chamber 112 back towards the top dead center position, i.e., a compression stroke of piston head 116. It should be understood that linear compressor 100 may include an additional piston head and/or additional chamber at an opposite end of linear compressor 100. Thus, linear compressor 100 may have multiple piston heads in alternative exemplary embodiments.
Linear compressor 100 also includes an inner back iron assembly 130. Inner back iron assembly 130 is positioned in the stator of the motor. In particular, outer back iron 150 and/or driving coil 152 may extend about inner back iron assembly 130, e.g., along the circumferential direction C. Inner back iron assembly 130 extends between a first end portion 132 and a second end portion 134, e.g., along the axial direction A.
Inner back iron assembly 130 also has an outer surface 137. At least one driving magnet 140 is mounted to inner back iron assembly 130, e.g., at outer surface 137 of inner back iron assembly 130. Driving magnet 140 may face and/or be exposed to driving coil 152. In particular, driving magnet 140 may be spaced apart from driving coil 152, e.g., along the radial direction R by an air gap AG. Thus, the air gap AG may be defined between opposing surfaces of driving magnet 140 and driving coil 152. Driving magnet 140 may also be mounted or fixed to inner back iron assembly 130 such that an outer surface 142 of driving magnet 140 is substantially flush with outer surface 137 of inner back iron assembly 130. Thus, driving magnet 140 may be inset within inner back iron assembly 130. In such a manner, the magnetic field from driving coil 152 may have to pass through only a single air gap (e.g., air gap AG) between outer back iron 150 and inner back iron assembly 130 during operation of linear compressor 100, and linear compressor 100 may be more efficient than linear compressors with air gaps on both sides of a driving magnet.
As may be seen in
A piston flex mount 160 is mounted to and extends through inner back iron assembly 130. A coupling 170 extends between piston flex mount 160 and piston assembly 114, e.g., along the axial direction A. Thus, coupling 170 connects inner back iron assembly 130 and piston assembly 114 such that motion of inner back iron assembly 130, e.g., along the axial direction A or the second axis A2, is transferred to piston assembly 114. Piston flex mount 160 defines an input passage 162 that permits refrigerant to flow therethrough.
Linear compressor 100 may include various components for permitting and/or regulating operation of linear compressor 100. In particular, linear compressor 100 includes a controller (not shown) that is configured for regulating operation of linear compressor 100. The controller is in, e.g., operative, communication with the motor, e.g., driving coil 152 of the motor. Thus, the controller may selectively activate driving coil 152, e.g., by supplying voltage to driving coil 152, in order to compress refrigerant with piston assembly 114 as described above.
The controller includes memory and one or more processing devices such as microprocessors, CPUs or the like, such as general or special purpose microprocessors operable to execute programming instructions or micro-control code associated with operation of linear compressor 100. The memory can represent random access memory such as DRAM, or read only memory such as ROM or FLASH. The processor executes programming instructions stored in the memory. The memory can be a separate component from the processor or can be included onboard within the processor. Alternatively, the controller may be constructed without using a microprocessor, e.g., using a combination of discrete analog and/or digital logic circuitry (such as switches, amplifiers, integrators, comparators, flip-flops, AND gates, field programmable gate arrays (FPGA), and the like) to perform control functionality instead of relying upon software.
Linear compressor 100 also includes a spring assembly 120. Spring assembly 120 is positioned in inner back iron assembly 130. In particular, inner back iron assembly 130 may extend about spring assembly 120, e.g., along the circumferential direction C. Spring assembly 120 also extends between first and second end portions 102 and 104 of casing 110, e.g., along the axial direction A. Spring assembly 120 assists with coupling inner back iron assembly 130 to casing 110, e.g., cylinder assembly 111 of casing 110. In particular, inner back iron assembly 130 is fixed to spring assembly 120 at a middle portion 119 of spring assembly 120.
During operation of driving coil 152, spring assembly 120 supports inner back iron assembly 130. In particular, inner back iron assembly 130 is suspended by spring assembly 120 within the stator or the motor of linear compressor 100 such that motion of inner back iron assembly 130 along the radial direction R is hindered or limited while motion along the second axis A2 is relatively unimpeded. Thus, spring assembly 120 may be substantially stiffer along the radial direction R than along the axial direction A. In such a manner, spring assembly 120 can assist with maintaining a uniformity of the air gap AG between driving magnet 140 and driving coil 152, e.g., along the radial direction R, during operation of the motor and movement of inner back iron assembly 130 on the second axis A2. Spring assembly 120 can also assist with hindering side pull forces of the motor from transmitting to piston assembly 114 and being reacted in cylinder assembly 111 as a friction loss.
The various mechanical and electrical parameters or constants of linear compressor 100 may be established or determined in any suitable manner. For example, the various mechanical and electrical parameters or constants of linear compressor 100 may be established or determined using the methodology described in U.S. Patent Publication No. 2016/0215772, which is hereby incorporated by reference in its entirety. For example, the methodology described in U.S. Patent Publication No. 2016/0215772 may be used to determine or establish a spring constant of spring assembly 120, a motor force constant of the motor of linear compressor 100, a damping coefficient of linear compressor 100, a resistance of the motor of linear compressor 100, an inductance of the motor of linear compressor 100, a moving mass (such as mass of piston assembly 114 and inner back iron assembly 130) of linear compressor 100, etc. Knowledge of such mechanical and electrical parameters or constants of linear compressor 100 may improve performance or operation of linear compressor 100. In alternative exemplary embodiments, a manufacturer of linear compressor 100 may provide nominal values for the various mechanical and electrical parameters or constants of linear compressor 100. The various mechanical and electrical parameters or constants of linear compressor 100 may also be measured or estimated using any other suitable method or mechanism.
As may be seen in
Current controller 710 may be the primary control for operation of linear compressor 100 during method 700. Current controller 710 is configured for adjusting the supply voltage voutput to linear compressor 100. For example, current controller 710 may be configured to adjust a peak voltage or amplitude of the supply voltage voutput to linear compressor 100. Current controller 710 may adjust the supply voltage voutput in order to reduce a difference or error between a peak current, ia,peak, supplied to linear compressor 100 and a reference peak current ia,ref. The peak current ia,peak may be measured or estimated utilizing any suitable method or mechanism. For example, an ammeter may be used to measure the peak current ia,peak. The voltage selector of current controller 710 may operate as a proportional-integral (PI) controller in order to reduce the error between the peak current ia,peak and the reference peak current ia,ref. At a start of method 700, the reference peak current ia,ref may be a default value, and clearance controller 730 may adjust (e.g., increase or decrease) the reference peak current ia,ref during subsequent steps of method 700, as discussed in greater detail below, such that method 700 reverts to current controller 710 in order to adjust the amplitude of the supply voltage voutput and reduce the error between the peak current ia,peak supplied to linear compressor 100 and the adjusted reference peak current ia,ref from clearance controller 730.
As shown in
Resonance controller 720 is configured for adjusting the supply voltage voutput. For example, when activated or enabled, resonance controller 720 may adjust the phase or frequency of the supply voltage voutput in order to reduce a phase difference or error between a reference phase, φref, and a phase between (e.g., zero crossings of) an observed velocity, {circumflex over (v)} or {circumflex over ({dot over (x)})}, of the motor linear compressor 100 and a current, ia, induced in the motor of linear compressor 100. The reference phase φref may be any suitable phase. For example, the reference phase φref may be ten degrees. As another example, the reference phase φref may be one degree. Thus, resonance controller 720 may operate to regulate the supply voltage voutput in order to drive the motor linear compressor 100 at about a resonant frequency. As used herein, the term “about” means within five degrees of the stated phase when used in the context of phases.
For the resonance controller 720, the current ia induced in the motor of linear compressor 100 may be measured or estimated utilizing any suitable method or mechanism. For example, an ammeter may be used to measure the current ia. The observed velocity {circumflex over ({dot over (x)})} of the motor linear compressor 100 may be estimated or observed utilizing an electrical dynamic model for the motor of linear compressor 100. Any suitable electrical dynamic model for the motor of linear compressor 100 may be utilized. For example, the electrical dynamic model for the motor of linear compressor 100 described above for step 610 of method 600 may be used. The electrical dynamic model for the motor of linear compressor 100 may also be modified such that
A back-EMF of the motor of linear compressor 100 may be estimated using at least the electrical dynamic model for the motor of linear compressor 100 and a robust integral of the sign of the error feedback. As an example, the back-EMF of the motor of linear compressor 100 may be estimated by solving
{circumflex over (f)}=(K1+1)e(t)+∫t
where
where
As shown in
The threshold phase error may be any suitable phase. For example, the voltage selector of resonance controller 720 may utilize multiple threshold phase errors in order to more finely or accurately adjust the phase or frequency of the supply voltage voutput to achieve a desired frequency for linear compressor 100. For example, a first threshold phase error, a second threshold phase error and a third threshold phase error may be provided and sequentially evaluated by the voltage selector of resonance controller 720 to adjust the frequency during method 700. The first phase clearance error may be about twenty degrees, and resonance controller 720 may successively adjust (e.g., increase or decrease) the frequency by about one hertz until the error between the reference phase φref and the phase between the observed velocity {circumflex over ({dot over (x)})} and the current ia is less than the first threshold phase error. The second threshold phase error may be about five degrees, and resonance controller 720 may successively adjust (e.g., increase or decrease) the frequency by about a tenth of a hertz until the error between the reference phase φref and the phase between the observed velocity {circumflex over ({dot over (x)})} and the current ia is less than the second threshold phase error. The third threshold phase error may be about one degree, and resonance controller 720 may successively adjust (e.g., increase or decrease) the frequency by about a hundredth of a hertz until the error between the reference phase φref and the phase between the observed velocity {circumflex over ({dot over (x)})} and the current ia is less than the third threshold phase error. As used herein, the term “about” means within ten percent of the stated frequency when used in the context of frequencies.
Clearance controller 730 is configured for adjusting the reference peak current ia,ref. For example, when activated or enabled, clearance controller 730 may adjust the reference peak current ia,ref in order to reduce a difference or error between an observed clearance, ĉ, of the motor of linear compressor 100 and a reference clearance, cref. Thus, clearance controller 730 may operate to regulate the reference peak current ia,ref in order to drive the motor linear compressor 100 at about a particular clearance between piston head 116 and discharge valve assembly 117. The reference clearance cref may be any suitable distance. For example, the reference clearance cref may be about two millimeters, about one millimeter or about a tenth of a millimeter. As used herein, the term “about” means within ten percent of the stated clearance when used in the context of clearances.
As shown in
The threshold clearance error may be any suitable clearance. For example, the voltage selector of clearance controller 730 may utilize multiple threshold clearance errors in order to more finely or accurately adjust the supply voltage voutput to achieve a desired clearance. In particular, a first threshold clearance error, a second threshold clearance error and a third threshold clearance error may be provided and sequentially evaluated by the voltage selector of clearance controller 730 to adjust a magnitude of a change to the current ia during method 700. The first threshold clearance error may be about two millimeters, and clearance controller 730 may successively adjust (e.g., increase or decrease) the current ia by about twenty milliamps until the error between the observed clearance ĉ of the motor of linear compressor 100 and the reference clearance cref is less than the first threshold clearance error. The second threshold clearance error may be about one millimeter, and clearance controller 730 may successively adjust (e.g., increase or decrease) the current ia by about ten milliamps until the error between the observed clearance ĉ of the motor of linear compressor 100 and the reference clearance cref is less than the second threshold clearance error. The third threshold clearance error may be about a tenth of a millimeter, and clearance controller 730 may successively adjust (e.g., increase or decrease) the current ia by about five milliamps until the error between the observed clearance ĉ of the motor of linear compressor 100 and the reference clearance cref is less than the third threshold clearance error. As used herein, the term “about” means within ten percent of the stated current when used in the context of currents.
As discussed above, current controller 710 determines or regulates the amplitude of the supply voltage voutput when the error between the peak current ia,peak and the reference peak current ia,ref is greater than (e.g., or outside) a threshold current error. By modifying the reference peak current ia,ref, clearance controller 730 may force the error between the peak current ia,peak and the reference peak current ia,ref to be greater than (e.g., or outside) the threshold current error. Thus, priority may shift back to current controller 710 after clearance controller 730 adjusts the reference peak current ia,ref, e.g., until current controller 710 again settles the current induced in the motor of linear compressor 100 as described above.
It should be understood that method 700 may be performed with the motor of linear compressor 100 sealed within a hermitic shell of linear compressor 100. Thus, method 700 may be performed without directly measuring velocities or positions of moving components of linear compressor 100. Utilizing method 700, the supply voltage voutput may be adjusted by current controller 710, resonance controller 720 and/or clearance controller 730 in order to operate the motor of linear compressor 100 at a resonant frequency of the motor of linear compressor 100 without or limited head crashing. Thus, method 700 provides robust control of clearance and resonant tracking, e.g., without interference and run away conditions. For example, current controller 710 may be always running and tracking the peak current ia,peak, e.g., as a PI controller, and resonant controller 720 and clearance controller 730 provide lower priority controls, with resonant controller 720 having a higher priority relative to clearance controller 730.
At step 910, the motor (e.g., driving coil 152) of linear compressor 100 is supplied with a time varying voltage, e.g., by the controller of linear compressor 100. Any suitable time varying voltage may be supplied to the motor of linear compressor 100, and the time varying voltage at step 910 may have a peak motor voltage, Vp, and an excitation frequency, f. At 920, a peak motor current, ip, may be measured while the time varying voltage is supplied to the motor of linear compressor 100. An ammeter or any other suitable method or mechanism may be used to measure the peak motor current ip.
At 930, an observed minimum velocity of the motor of linear compressor 100 is calculated. As an example, the observed minimum velocity may be obtained using the methodology described in U.S. Patent Publication No. 2016/0215770, which is hereby incorporated by reference in its entirety. Thus, the observed minimum velocity {dot over (x)}min
After step 930, a set of predictors is established. The set of predictors may include the peak motor voltage Vp, the excitation frequency f, the peak motor current ip, the observed minimum velocity the observed stroke length SLo, etc. The set of predictors may also include each product between two of the peak motor voltage Vp, the excitation frequency f, the peak motor current ip, the observed minimum velocity {dot over (x)}min
At step 940, redundant predictors from the set of predictors are removed in order to establish a reduced set of predictors. An example, covariance testing may be conducted on the set of predictors in order to establish a reduced set of predictors by removing highly correlated predictors from the set of predictors. After removing redundant predictors, the reduced set of predictors may include or consist of the peak motor voltage Vp, the excitation frequency f, the peak motor current ip, the observed minimum velocity {dot over (x)}min
It will be understood that various operating parameters of the linear compressor 100 may be modified to provide suitable data and/or measurements for the predictors within the set of predictors. For example, a peak current, a suction pressure and/or a discharge pressure of the linear compressor 100 may be adjusted to provide data and/or measurements for the predictors within the set of predictors across a variety of operating conditions for linear compressor 100. By varying the operating parameters of the linear compressor 100 and collecting data and/or measurements for the predictors within the set of predictors, performance of method 900 to estimate head clearance of linear compressor 100 may be improved.
At step 940, a model is established for an estimated head clearance of linear compressor 100 with the reduced set of predictors. The model for the estimated head clearance of linear compressor 100 may be established at step 940 by conducting a best subsets regression with the reduced set of predictors from step 930. As an example, the model for the estimated head clearance of linear compressor 100 may be a linear combination of each predictor of the reduced set of predictors. Thus, each predictor from the reduced set of predictors may be multiplied by a respective coefficient. The linear combination may also include a constant. At step 950, the coefficients of the model for the estimated head clearance of linear compressor 100 may be calculated. The coefficients of the model for the estimated head clearance of linear compressor 100 may be calculated using a least-squares method, e.g., and measured head clearance values.
The model for the estimated head clearance of linear compressor 100 from step 940 and the coefficients from step 950 may be saved in the memory of the controller of linear compressor 100. Thus, the model for the estimated head clearance of linear compressor 100 may be used by the controller during operation of linear compressor 100, e.g., to adjust operation of linear compressor towards a desired head clearance, such as the reference clearance cref of the clearance controller 730. Thus, the desired head clearance may be established and the peak motor current ip and/or peak motor voltage Vp may be adjusted until the estimated head clearance of the linear compressor from the model for the estimated head clearance of linear compressor 100 is about equal to the desired head clearance.
The model for the estimated head clearance of linear compressor 100 may be used with the clearance controller 730 to adjust operation of linear compressor 100, with the estimated head clearance from the model for the estimated head clearance of linear compressor 100 corresponding to the observed clearance ĉ described above. The motor of linear compressor 100 may be sealed within the hermetic shell during operation of the linear compressor 100 with the clearance controller 730. Thus, by generating and using the model for the estimated head clearance of linear compressor 100, a sensor to directly measure an actual head clearance during operation of linear compressor 100 may not be included or required.
This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they include structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.